https://ntrs.nasa.gov/search.jsp?R=20100035087 2019-08-30T11:55:35+00:00Z FEATHERSAIL – THE NEXT GENERATION OF NANO-CLASS SAIL VEHICLE D.C. Alhorn Marshall Space Flight Center (MSFC) Huntsville, Alabama ABSTRACT Solar sail propulsion is a concept, which will soon become a reality. Solar sailing is a method of space flight propulsion, which utilizes the light photons to propel spacecrafts through the vacuum of space. Solar sail vehicles have generally been designed to have a very large area. This requires significant time and expenditures to develop, test and launch such a vehicle. Several notable solar propulsion missions and experiments have been performed and more are still in the development stage. This concept will be tested in the near future with the launch of the NanoSail-D satellite. NanoSail-D is a nano-class satellite, <10kg, which will deploy a thin lightweight sheet of reflective material used to propel the satellite in its low earth orbit. The NanoSail-D solar sail design is used for the basic design concept for the next generation of nano- class solar sail vehicles. The FeatherSail project was started to develop a solar sail vehicle with the capability to perform attitude control via rotating or feathering the solar sails. In addition to using the robust deployment method of the NanoSail-D system, the FeatherSail design incorporates other novel technologies. These technologies include deployable thin film solar arrays and low power, low temperature Silicon-Germanium electronics. Together, these three technological advancements provide a starting point for smaller class sail vehicles. These smaller solar sail vehicles provide a capability for inexpensive missions to explore beyond the realms of low earth orbit. INTRODUCTION BACKGROUND Johannes Kepler envisioned the possibility of sailing through the expanse of the universe on ships rigged with sails that would capture the heavenly breezes. Since then many have postulated different methods of capturing the solar photon flow and using that for spacecraft propulsion. The first time the idea was tested as a space a propulsion method was with Mariner 10 in 1974 when the satellite’s fuel supply was low on its trip to Mercury. Scientists angled the solar panels to utilize the propulsion from the photons in the same method that solar sails work. Although Mariner 10 was not designed for solar sailing, the propulsion was sufficient to maintain Mariner’s course. More recently, there have been multiple designs specifically created to prove the propulsion while in Low Earth Orbit (LEO). These include missions assembled by Japan Aerospace Exploration Agency (JAXA), the Planetary Society, and NASA. JAXA sent a “cloverleaf sail” into a very low orbit (169 km) in August of 2004. Unfortunately at this altitude, the atmospheric drag is large which makes solar propulsion hard to detect. COSMOS 1 was a large- scale solar sail assembled by the Planetary Society to prove the concept of solar sailing at a much higher altitude. This device was to deploy eight triangular sails; each would contain 600 square meters making a total of 4800 square meters. To avoid as much atmospheric drag as possible, COSMOS 1 was to be deployed at 800 kilometers. Unfortunately, the Russian rocket, which COSMOS 1 was riding on, failed to reach orbit, and thus, the satellite and sail system were never tested in orbit. Approved for public release; distribution is unlimited Marshall Space Flight Center, Export Control Authority, Amelia Oneil ES13 NASA’s Marshall Space Flight Center concluded in 2006 its solar sail mission development project under NASA’s New Millennium program. The ST9-SSM project was an ambitious development of a 20m sail for ground deployment. Although this project did not continue after the ground tests, it did provide a learning experience for the solar sail community. In 2007, a small group of engineers at MSFC began a sail development for a nano-class satellite. Nano-satellites are typically < 10kg and have limited capabilities. Thus the CubeSail project started in hopes of developing a precursor demonstration mission. In early 2008, the CubeSail project was offered a flight opportunity and thus the NanoSail-D flight program began. The goal of the NanoSail-D project was to quickly deliver the sail subsystem that was envisioned with the CubeSail effort. After an intense four-month effort, two satellites were designed, manufactured and tested. The launch vehicle for the NanoSail-D mission was the third launch of SpaceX’s Falcon 1 rocket. In August 2008, the dream of solar sails was about to be realized. Unfortunately, like the Cosmos 1 mission, the rocket failed to reach orbit resulting in the loss of the first NanoSail-D unit. RECENT DEVELOPMENTS In April 2009, another flight opportunity was presented for the NanoSail-D second unit. NanoSail-D2 will be flown on the STP-S26 mission and is currently scheduled for mid 2010 launch date. During launch, NanoSail-D2 will be stored aboard the FASTSAT-HSV01 satellite. NanoSail-D2 will be ejected from the parent satellite sometime after the parent has been checked out and conditions are correct for ejection. It is expected that the NanoSail-D2 satellite will remain in orbit about 70-100 days. This limited orbital lifetime is due to the atmospheric drag at the expected orbit altitude. Figure 1 is a photograph of the NanoSail-D sail during ground deployment set on an earth orbit background for artistic effect. There are many new solar sail missions planned for the near future. JAXA launched and deployed a large solar sail in June of 2010 to venture on an interplanetary mission. This spacecraft is known as Ikaros (Interplanetary Kite-craft Accelerated by Rays Of the Sun). “The square Ikaros sail, with a diagonal diameter of 66 feet, contains thin film solar cells to generate electricity. The spacecraft will spin up to about 20 rpm for stability during its mission.” Figure 2 is an artist’s conceptual picture of the Ikaros sail. Ikaros is a secondary payload, which will be traveling to Jupiter on a six-month journey Figure 1. NASA’s NanoSail-D Figure 2. Artist’s concept of JAXA’s Ikaros Photo courtesy of NASA. Photo courtesy of JAXA The Planetary Society has recently received funding for their “LightSail” project. This project will consist of three different sail missions starting with the first deployment in 2010. The first of these, named LightSail-1, will be very similar to NanoSail-D both in size and boom design. The second flight will carry a sail capable of increasing the altitude of the sail’s orbit by increasing orbital speed. Finally, the third sail would have the capability to break out of earth orbit where solar sails are said to perform best. Also there has been rumors of a COSMOS-2 mission, but the Planetary Society’s major efforts are currently focused on the LightSail project. NEXT GENERATION OF SAIL VEHICLE DESIGN CONSIDERATIONS All of the previous sail vehicle projects have the same goal. Proving the deployment of the sail and determining the extent of solar propulsion. With the successful orbital NanoSail-D2 deployment, it necessary to focus on how to apply the design capabilities of the NanoSail-D system to the next generation of solar sail vehicles. The basic consideration for sail vehicles is the sail area density, or areal density. Areal density is the total vehicle mass divided by the total sail area. This basic parameter defines the capability of the concept to successfully perform many scientific and research missions. Figure 3 is a chart of the performance requirements from the ST9-SSM project. Figure 3. – Performance Requirements for Potential Solar Sail Missions Photo courtesy of NASA ST9-SSM When trying to go beyond a basic proof of concept, there are a few key issues addressed with the FeatherSail design. First, NanoSail-D had an aerial density of 380 g/m2 with an overall sail area of 10 m2. There is enough volume in the NanoSail-D sail compartment to store 40m2 of sail material. With longer booms, the areal density of a fully packaged NanoSail-D vehicle would approach the upper line on the previous chart. One design consideration is the limited mass available to the payload. Since the areal density must inherently be low, the payload and all avionics must be minimized. In deep space, the main considerations are power and the ability to survive the increased radiation subjected to the vehicle. Ikaros will attempt to solve the power problem by incorporating the solar cells in the sail material. The practicality of this method is yet to be determined. Another method is to lower the power consumption of the payload and miniaturize or limit the functions on a single vehicle. The next design issue to be considered is the ability to steer the vehicle. When the vehicle is in near earth orbit torque rods can be used with limited capability as the orbit increases. Reaction wheels and Control Momentum Gyroscopes (CMGs) can be used for attitude control, but there is a limit to which they can be used until they reach saturation or gimbal lock. Then there must be some other means to desaturate the reaction wheel or unlock the CMG. In low earth orbit, the common method is to use torque rods, but these are unusable in the orbits in which solar sail vehicles are not affected by atmospheric drag or out in deep space. Steerable sails give the vehicle the capability to not only provide for propulsion, but also control the attitude of the vehicle. This method provides an alternative to desaturate a reaction wheel or unlock a CMG. FEATHERSAIL – SECOND GENERATION NANOSAIL CONCEPT NanoSail-D2 will have the capability to prove solar propulsion, along with testing the sail deployment in a zero gravity environment.